see http://wiki.openstreetmap.org/wiki/Harbour#Outlines_of_the_harbour
and http://wiki.openstreetmap.org/wiki/Harbour#Breakwater
http://wiki.openstreetmap.org/wiki/Tag:man_made%3Dbreakwater
http://wiki.openstreetmap.org/wiki/Proposed_features/Breakwater

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HB: tag as "natural=coastline" as well?; is that valid for a single line?? perhaps not.
careful with coastline way direction! I'm not 100% sure but I think it should be connected but can go inland of the real coastline.
waterway=breakwater is talked about as an alternative but seems wrong to me. I prefer man_made=
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RP:i don't think we should use coastline, as it's not a natural object.
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Chathams uploaded 3 May 2010 (HB).
South and Stewart Islands uploaded 18 Dec 2010 (HB) in changeset 6691578.
North Island uploaded 18 Dec 2010 (HB) in changeset 6691733.